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How to Match Impedance

In radio communications, impedance matching is the process of matching electrical parameters of a transmitted signal to physical and electrical parameters of an antenna. A properly matched antenna ensures that the greatest amount of signal power reaches the antenna and gets into the air. Amateur radio operators, citizens band radio users, radio communications engineers and radio technicians use impedance matching to maximize the efficiency of their communications equipment. There are several ways to obtain resonance between a transmitter and an antenna. Use these methods to get the most signal from your radio into the air.

Things You'll Need

Standing wave ratio (SWR) meter
Short coaxial cable with connectors
Radio transmitter
Antenna

Instructions

- 1
  Connect the output of the your radio to the input of an SWR meter using a short piece of coaxial cable (coax).
- 2
  Connect the antenna feed line coax to the output of the SWR meter. Set the FWD/REV switch to the forward (FWD) position.
- 3
  Transmit a signal and adjust the set/adjust knob so the meter needle points to the "set" position on the meter.
- 4
  Switch the FWD/REV switch to the reverse (REV) position and note the reading on the meter. If this reading is 1.0 or close to 1.0 (under 1.5), your antenna is impedance matched to the transmitted signal with an SWR of 1:1 or under 1.5:1.
- 5
  If the SWR reading is greater than 1.5 to 1, or if you wish to obtain an SWR closer to 1:1, adjust your antenna until resonance is achieved.
- 6
  Shorten or lengthen your antenna or its elements to achieve a 1:1 SWR or as low an SWR as possible. Some antennas have a matching network (gamma match) which involves loosening a screw and sliding a clamp to achieve resonance on your desired output frequency instead of lengthening or shortening the antenna.
- 7
  Check the SWR again after making all other adjustments and installing the antenna in its final operating position. Check the SWR occasionally or leave the SWR meter in line to monitor SWR continuously to insure proper impedance matching at all times and under varying conditions such as weather.

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